This application is based on and claims priority to Japanese Patent Application No. 10-324303 filed Nov. 16, 1998.
1. Field of the Invention
This invention relates to an outboard motor cooling system, and more particularly to an improved cooling system for an oil pan that depends from an engine into a driveshaft housing of an outboard motor.
2. Description of Related Art
An outboard motor generally comprises a drive unit which includes a power head disposed at its top portion, a driveshaft housing depending from the power head and a lower unit further depending from the driveshaft housing. The power head incorporates a powering engine therein and a protective cowling encircling the engine. The driveshaft housing has a driveshaft extending from an output shaft of the engine and downwardly therethrough to the lower unit. The lower unit carries a propulsion device such as a propeller which is mounted on a propeller shaft driven by the driveshaft. The driveshaft housing and the lower unit further contain some sections of an exhaust system for discharging exhaust gasses from the engine outwardly. Actually, exhaust passages and expansion chambers are formed therein and exhaust gasses are discharged to the body of water surrounding the outboard motor through, for example, a hub of the propeller.
The outboard motor further comprises a bracket assembly which includes a swivel bracket and a clamping bracket. The swivel bracket carries the drive unit for pivotal movement about a steering axis extending generally vertically. The clamping bracket is mounted on a transom of an associated watercraft and supports the swivel bracket for pivotal movement about a tilt axis extending generally horizontally.
Some outboard motors recently have employed four-stroke engines as prime movers for such motors. One reason for this tendency is that emissions from a four-stroke engines is cleaner relative to a two-stroke crankcase compression engine. The four-stroke engine typically has a separate oil pan for lubrication of the engine, and usually the oil pan depend from the engine into the driveshaft housing of the outboard motor. Lubricant is pumped to the engine by a lubricant pump and oil drains to the oil pan after lubricating the engine. Because the engine commonly operate at high temperatures, the returning lubricant heats the oil pan.
The outboard motor has a cooling system for cooling the engine with coolant, usually water. More specifically, a water pump is provided in the cooling system and water pumped up by the water pump from the body of water surrounding the outboard motor is delivered to the engine. Conventionally, the cooling system utilizes the same water that has already cooled the engine to cool the oil pan. For this purpose, the oil pan is usually surround by a coolant pool through which the water that has circulated through at least a portion of the engine flows. The coolant pool is formed between an outer wall of the oil pan and an inner wall of the driveshaft. Because the water is already hot, however, the oil pan is not significantly cooled. As a result, an outer wall of the driveshaft is likely to be heated, and can become discolored. This harms the appearance of the outboard motor.
In addition, an exhaust manifold, which is one of the sections of the exhaust system, is positioned to pass through the oil pan. The exhaust gasses flowing through this exhaust manifold also are hot and further heat the oil pan. The heat sink provided by the water passing through the coolant pool in a conventional system therefore may not be sufficient to prevent discoloration of the driveshaft housing and overheating of the lubricant.
Other components of the outboard motor also are affected by the elevated temperature of the oil pan within the drive shaft housing. For instance, such heat may also affect an upper mount of the steering assembly. The steering assembly includes both an upper mount and a lower mount, which are affixed on the drive unit to pivotally support it on the swivel bracket. A steering shaft extends through forward portions of the respective mounts and a steering shaft housing disposed at the rear of the swivel bracket. Rear portions of the respective mounts are affixed to the forward portion of the driveshaft housing so as to be spaced apart vertically from each other. The rear portions contain elastic elements to absorb vibrations generated by the engine and the propeller or shocks exerted upon the drive unit, and to prevent transfer of such to the associated watercraft. The upper mount is usually positioned above and in the proximity to the oil pan. The elastic members of the upper mount tends to be deteriorated by heat transferred from the oil pan. Other components, particularly electrical components, within the protective cowling may be also damaged by the heat.
The present outboard motor cooling system enhances cooling of the oil pan vis-a-vis conventional outboard motor cooling systems. The cooling system also desirably inhibits discoloration of a driveshaft housing of the outboard motor, as well as deterioration of components positioned above the oil pan, such as, for example, but without limitation, elastic members of an upper mount and engine components.
In accordance with one aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes a periphery coolant jacket generally surrounding the oil pan and being supplied with coolant that has not cooled the engine. The cooling system further includes a coolant discharge jacket bypassing the periphery coolant jacket. Coolant that has cooled the engine passes through the coolant discharge jacket.
In accordance with another aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes an upstanding coolant passage extending generally vertically through the oil pan and the cooling system supplies coolant to the engine through the upstanding coolant passage.
In accordance with an additional aspect of the present invention, an outboard motor comprises a power head having an internal combustion engine. A housing depends from the power head and supports a propulsion device driven by the engine for propelling an associated watercraft. An oil pan contains lubricant for lubrication of the engine. The oil pan depends into the housing and is spaced from the housing. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes a coolant pool defined between the oil pan and the housing. The cooling system supplies coolant that has not cooled the engine to the coolant pool. The cooling system further includes a coolant discharge jacket bypassing the coolant pool. Coolant that has cooled the engine passes through the coolant discharge jacket.
In accordance with another aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. An exhaust system is provided for discharging exhaust gasses from the engine. The exhaust system includes an exhaust passage that passes through the oil pan. A cooling system is provided for cooling at least the engine and the oil pan. The cooling system includes means for forming a heat sink between the exhaust passage and the oil pan when the engine is operated. In this manner, the amount of heat transfer between the exhaust passage and the oil pan is reduced, i.e., the oil pan and the exhaust passage generally are thermally decoupled from each other.
In accordance with yet another aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system cools at least the engine and the oil pan. The cooling system includes a lower transverse coolant jacket that extends generally transversely below the oil pan. The cooling system supplies coolant that has not cooled the engine. The cooling system further includes a coolant discharge jacket bypassing the lower transverse coolant jacket. Coolant that has cooled the engine passes through the coolant discharge jacket.
In accordance with a further aspect of the present invention, an outboard motor comprises an internal combustion engine. An oil pan depends from the engine and contains lubricant for lubrication of the engine. A cooling system cools at least the engine and the oil pan. The cooling system includes an upper transverse coolant jacket extending generally transversely above the oil pan. The cooling system supplies coolant that has not cooled the engine. The cooling system further includes a coolant discharge jacket bypassing the upper transverse coolant jacket. Coolant that has cooled the engine passes through the coolant discharge jacket.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follow.